An electrodeless fluorescent lamp (10) having a burner (20), a ballast housing (30) containing a ballast (40) and a screw base (50) for connection to a power supply. A reentrant cavity (60) is formed in the burner (20) and an amalgam receptacle (70) containing amalgam (75) is formed as a part of the reentrant portion and in communication with the burner (20). A housing cap (80), formed of a suitable plastic, connects the burner (20) to the ballast housing (30) and a suitable adhesive (31) fixes the burner to the housing cap (80). An EMI cup (90) is formed as an insert to fit into the ballast housing (30), which also is formed of a suitable plastic, and has a bottom portion (100) and an EMI cap (110) with an aperture (120) therein closing an upper portion (140). The EMI cup (90) and the EMI cap (110) are preferably formed from 0.5 mm brass. The amalgam receptacle (70) extends through the aperture (120) and into the cup (90). For a fixed amalgam position, changing the aperture size allows adjustment of the amalgam tip temperature, and thus, allows control of the system lumen output, efficacy, CCT and CRI, all of which are dependent on the amalgam temperature.